Close up filter +1 (NO1) question..

[intotherainbow]

I've recently bought it, and I do notice the different between using it and not using it, but it's very small! I did some research and know that there are some type of close up filter, that have more diop (+4, or +10)

My question is why do they make the +1 ones when they almost do nothing here?

 

[Donki]

Are they not usually sold in 3's so that they can be stacked for different magnifications?